Accumulative line graph or Lorenz curve

 The Lorenz curve is used in economics and ecology to describe inequality in wealth or size. It is a graphical representation of the cumulative distribution function of a probability distribution. It is practical in relating inequality among the size of individuals in ecology and also useful to represent income distribution. The graph below shows the proportion of income going to the poorest people, middle-class people and wealthiest people.

http://www.squarecirclez.com/blog/the-gini-coefficient-of-wealth-distribution/4187